Fluorescence behaviour of an anthracene–BODIPY system affected by spin states of a dioxolene–cobalt centre

Abstract

Dioxolene cobalt complexes, [Co(L)(TPA)]PF₆ (1) and [Co(L)(Me₃TPA)]PF₆ (2), were synthesized using a catechol with anthracene and boron-dipyrromethene (BODIPY), H₂L, and tris(pyridin-2-ylmethyl)amine (TPA) or tris[(6-methylpyridin-2-yl)methyl]amine (Me₃TPA) and characterised by UV-vis absorption, IR and NMR spectroscopy. Complexes 1 and 2 are a low-spin cobalt(III) catecholate form and a high-spin cobalt(II) semiquinonate form, respectively, in CH₃CN at room temperature. The effect of the spin states of the dioxolene–cobalt centre on fluorescence was investigated in CH₃CN at room temperature. The fluorescence intensity of 1 was clearly lower than that of 2, although both complexes showed weaker fluorescence compared with that of H₂L. The difference in the intensity between 1 and 2 is mainly due to the enhancement of nonradiative decay processes based on the stronger metal–ligand interactions for the cobalt(III) catecholate form of 1 compared with the cobalt(II) semiquinonate form of 2.